Switched-mode power supply units in different models are widely known. Compared with other power supply types such as, especially, conventional transformer power supplies, switched-mode power supplies have a relatively high efficiency. In addition, switched-mode power supply units have a relatively large range of tolerance for input voltages and frequencies, a smaller constructional size and less expensive production costs compared with conventional power supplies.
Theoretically, switched-mode power supply units, due to their switching principle, only transfer the power actually needed on the secondary side. Known switched-mode power supply units therefore have an efficiency of often over 90% within an operating range of about 20 to 100% of their nominal output power. Unfortunately, the efficiency of known switched-mode power supply units drops considerably especially below 20% of the nominal output power. Among other things, this is caused by chopping the input voltage on the primary side, due to the principle, and the associated switching losses.
It is especially in the case of computers and similar devices which, on the one hand, require a relatively large input power in operation, but only consume a greatly reduced input power in a quiescent, energy-saving or standby mode, that this represents a problem with respect to the energy efficiency of the switched-mode power supply units used.
It could therefore be helpful to provide a power supply unit and a method of operation for a power supply unit which provides for high energy efficiency over a wide range of possible output powers. In particular, it could be helpful for the energy efficiency in the lower range of a nominal output power to be improved compared to known switched-mode power supply units.